1. Field of the Invention
The present invention generally relates to a surface acoustic wave device for a resonator and a band-pass, or other similar electronic components, for example, and more particularly to a surface acoustic wave device having superior stable temperature characteristics.
2. Description of the Related Art
Surface acoustic wave devices are widely used as band-pass filters or resonators. Such surface acoustic wave devices are required to include a piezoelectric substrate having a large electromechanical coupling coefficient. Also required for some applications is a surface acoustic wave device having increased resistance against possible temperature variations.
Conventionally, an ST-cut quartz substrate, an LST-cut quartz substrate and the like are well known for use as such a piezoelectric substrate having superior stable temperature characteristics.
Japanese Patent Publication (Kokoku) No. 61-45892 discloses a surface acoustic wave device which has improved temperature characteristics by disposing on a rotated Y-cut quartz substrate an interdigital electrode made of Au in such a way that the X-axis of the substrate and the surface acoustic wave propagating direction define an angle of about 90 degrees therebetween.
However, the conventional ST-cut quartz substrate and LST-cut quartz substrates suffer from a problem of an insufficient electromechanical coupling coefficient, although these devices may provide good temperature characteristics.
The prior art surface acoustic wave device as disclosed in Japanese Patent Publication No. 61-45892 experiences an additional problem of increased costs due to the fact that its interdigital transducer is made of Au. Further, another problem associated with the prior art is that the manufacturing process is complicated due to the necessity of using an undercoat layer such as Cr or the like because Au has less adhesion strength for adhering to the substrate used.
For the aforementioned reasons, the inventors discovered that there is a need for a surface acoustic wave device having superior stable temperature characteristics and a large electromechanical coupling coefficient and which is adapted to be produced at a low cost.